How many E. coli = 1 O.D. unit?

[Zophonias O. Jonsson]

 In article <3sb250$nbu at riscsm.scripps.edu>, "Edward K.L. Chan"
<echan at scripps.edu> says:
>
>Hi netters,
>   I wonder if someone may be able to provide a reliable formula to calculate
>the number of DH5-alpha or XL1-Blue based on O.D. measurement.  Thanks in 
>advance.

I have seen various conflicting values for estimating E. coli titers from
OD600.  They differ by more than an order of magnitute.  Of course there
must be some strain variance but I doubt that it can be that much.  The
values that I trust best are from a titration done by Sigridur H.
Thorbjarnardottir at the University of Iceland (since I know she is a
master in handling E. coli).  

Doing a linear regression to her points I get the following equation:

Number of TG1/ml = 9.3 E8 x OD600

This should give a reasonable estimate, at least from OD600 = 0.1 to 0.8,
I don't guarantee higher values, you'll have to find that out for
yourself.

Hope this helps

Zophonias

_____________________________________________________________________
Zophonias O. Jonsson
Institut fur Veterinarbiochemie               Tel: (41-1)-257-54-75
Universitat Zurich-Irchel                     Fax: (41-1)-362-05-01
Winterthurerstrasse 190
CH-8057 Zurich
Switzerland
_____________________________________________________________________